Method for modifying the surface of an abrading wheel

ABSTRACT

The surface configuration of a tapered abrading wheel is modified to provide a straight line of intersection between two tapered abrading wheels when those abrading wheels are mounted for rotation about parallel axes by fixing the axis of the abrading wheel at a location parallel to a line that does not intersect and is not parallel to the axis of the dressing wheel, and relating the axis of a dressing wheel to that line such that rotation of the axis of the dressing wheel about that line would generate a true hyperboloid of revolution, and then simultaneously rotating the abrading and dressing wheels while the surfaces of the abrading and dressing wheels are in contact to modify the surface of the abrading wheel and produce a surface that closely approximates a portion of a true hyperboloid of revolution.

' United States Patent [72] Inventor Warren 1. Nissen [56] References Cited 1 N gopsgield, Mass. UNITED STATES PATENTS [21] P 72 1,867,939 7/1932 Davenport 125/11 [22] 1969 2 422 47s 6/1947 Devlie 51/95ux Division of Ser, No. 568,873, Oct. 14, 1966, M1901 yes 5l/225X Patent No. 3,461,616. [45] Patented Mar. 1971 1,496,922 6/1924 Conners 125/11UX 7 3 Assignee The Gillette Company Primary Examiner-Harold D. Whitehead Boston, Mass Attorney-Willis M. Ertman ABSTRACT: The surface configuration of a tapered abrading wheel is modified to provide a straight line of intersection between two tapered abrading wheels when those abrading wheels are mounted for rotation about parallel axes by fixing the axis of the abrading wheel at a location parallel to a line [54] fagggg gg THE SURFACE OF AN that does not intersect and is not parallel to the axis of the 2 Cl 11 D dressing wheel, and relating the axis of a dressing wheel to that aims rawmg line such that rotation of the axis of the dressing wheel about [52] U.S. Cl 125/11, that line would generate a true hyperboloid of revolution, and 51/287 then simultaneously rotating the abrading and dressing wheels [51] Int. Cl ..B24b 53/00, while the surfaces of the abrading and dressing wheels are in B24b 1/00 contact to modify the surface of the abrading wheel and 50] Field of Search 125/ l 1; produce a surface that closely approximates a portion of a true hyperboloid of revolution.

'PATENIEUHAR 2197! Q sum 2 BF 3 FIG n w FIG 7 PATENTED MAR 2 I97! SHEEI 3 OF 3 FIG 8 METHOD FOR MODIFYING THE SURFACE OF AN ABRADING WHEEL This application is a division of our copending patent application Ser. No. 586,873, filed Oct. 14, 1966 now US. Pat. No. 3,461,616 dated Aug. 19, 1969.

This invention relates to methods and apparatus for producing an extremely sharp and durable cutting edge on a razor blade or similar cutting tool, and to improved razor blades manufactured in accordance with the methods and apparatus of the invention.

The sharpening of razor blades by mass production techniques involves a series of abrading operations (grinding and honing) to produce the desired sharp and durable shaving edge. Each abrading operation forms a facet on the blade edge being sharpened, which facet is modified by subsequent abrading operations of increasing fineness. In these series of abrading operations, it is essential to minimize possible damage to the ultimate tip of the blade edge while providing a uniform edge of the desired durability. A particular problem relates to so-called spot turn defects which are produced at the end of the last abrading operation. Also, in certain razor blades, it is desirable that the thickness of the sharpened edge of the blade be minimized as a relatively thin edge appears to improve the shaveability characteristics of the blade. However, in order to provide adequate strength and durability of the blade, certain blade materials require a relatively large included angle at the ultimate tip of the sharpened edge. A par ticular example of such a blade material is flexible alloy steel material useful in a ribbon-type razor blade. Such steel interacts with abrading wheels in a manner that modifies the abrading characteristics of the abrading material.

In accordance with the invention claimed in US, Pat. No. 3,461,616 a facet on an edged cutting tool is formed by abrading in a manner such that the ultimate tip is abraded first and points increasingly remote from the ultimate tip are subsequently abraded in a manner that avoids further contact with the ultimate tip. It is also preferred to form the facets such that the included angle of the blade edge decreases as the distance along the facet surface from the ultimate tip increases, forming a facet surface of convex configuration. In the apparatus for forming these facet configurations, two abrading wheels of substantial axial length are disposed in juxtaposition so that their axes define a plane. The edge of the tool to be sharpened is then passed along a path inclined with respect to said plane so that the path approaches the plane along the direction of movement of the tool edge past the wheels.

In the preferred embodiment of that invention (the manufacture of high quality razor blades) convex facet surfaces are formed at a finish honing stage, subsequent to a grinding stage and a rough honing stage. Two juxtaposed finish honing abrasive wheels, each having a helical land formed in its circumferential surface, are mounted so that the two wheels are in interengagement and define a nip between them. The diameter of each wheel changes along its length so that the wheel is ef fectively tapered and therefore the angle between the abrasive surface at the intersection nip changes along the length of the assembled pair.

The angle of the plane defined by the axes of the honing wheels with respect to the path of the blade (tilt angle) may be varied over a substantial range but in particular embodiments, an' angle of at least about has been found to produce advantageous results. The range of angles of contact of the abrasive wheels with the edge being honed to convex facet surfaces may be changed for any given tilt angle, for example, by changing the length or diameter of the wheels or by changing the orientation of the axes of the wheels. The range of angle obtainable in the practice of the inventionextends from an entrance half angle of 60 to an exit half angle of 0. Generally, such an extended transition of contact angle is not necessary and in a particular embodiment an entrance half angle of 16 and an exit half angle of 7 has found to produce extremely satisfactory results. l

By employing the larger angle at the entrance end, it has been found that the disturbance of the ultimate tip of the blade may be reduced particularly at the end of its contact with the honing wheels, producing a blade edge of improved quality. This feature is particularly advantageous in the case of steel that includes alloying elements such as chromium or molybdenum, which change the interaction between the steel and the abrading wheel and the abrading characteristics of the wheel. Such a steel is the relatively soft alloy steel particularly useful for flexible blades of the type used in a ribbon-type razor. It will be understood that, while the invention has particular advantages in connection with the final honing operation on a ribbon-type razor blade, it may be used with other abrading steps in the formation of the sharpened edge of other types of razor blades and other cutting implements.

It is an object of this invention to provide novel and improved methods for modifying the surface of an abrading wheel.

A more specific object of this invention is to provide a method for modifying the surface of an abrading wheel to provide a straight line of intersection between two tapered abrading wheels when those abrading wheels are mounted for rotation about parallel axes.

In accordance with the invention, the surface configuration of a tapered abrading wheel is modified by providing a support for the abrading wheel adjacent the dressing wheel, offsetting the axis of the abrading wheel relative to the axis of the dressing wheel in vertical and horizontal directions and fixing the axis of said abrading wheel at a location parallel to a line that does not intersect and is not parallel to the axis of the dressing wheel, the dressingwheel axis being related to that line such that rotation of the dressingwheel axis about that line would generate a true hyperboloid of revolution; and simultaneously rotating said abrading and dressing wheels about their respective axes while the surfaces of said abrading and dressing wheels are in contact to modify the surface of the abrading wheel so that that surface closely approximates a portion of a true hyperboloid of revolution.

Other objects, features, and advantages of the invention will be seen as the following description of a particular embodiment thereof progresses in conjunction with the drawings, in which:

FIG. 1 is a diagrammatic side view of razor blade-sharpening apparatus employed in practicing the invention;

FIG. 2 is a diagrammatic top view of two finish honing wheels disposed in the configuration employed in the apparatus shown in FIG. 1 in the practice of the invention;

FIG, 3 is a diagrammatic side view of the finish honing wheel configuration shown in FIG. 2;

FIG. 4 is a diagrammatic end view of the finish wheel configuration shown in F IG.,2;

FIGS. 5 and 6 are diagrams of the configurations (enlarged 2400 times) of a conventionally sharpened edge of a razor blade and an edge of a razor blade sharpened in accordance with the invention respectively;

FIG. 7 is a geometric diagram illustrating a preferred. form of the contour and mounting of a finish honing wheel in the practice of the invention;

FIG. 8 is a schematic side view of structure for modifying the surface of the honing wheel for use in the apparatus shown inFIGS. 2-4;

FIGS. 9 and 10 are schematic top and end views respectively of the apparatus shown in FIG. 8; and

FIG. 11 is a geometric diagram indicating geometry for modifying a honing wheel surface by the apparatus shown in FIGS. 8-10.

There is shown in FIG. 1 in diagrammatic form, apparatus for sharpening the edge of a razor blade in accordance with the inventionThe razor blade 10, which inthis embodiment is in continuous strip form, of uniform width and its principal metallurgical constituents in addition to iron are 0.40 percent carbon and 13.5 percent chromium, is to have onlyone (its.

upper) edge 12 sharpened. This upper edge 12 is subjected to grinding operations at stage 14 by a pair of grinding wheels 16" mounted for rotation about axes 18; a rough honing operation at stage 20 by a pair of honing wheels 22 mounted for rotation about axes 24; and a finish honing operation at stage 26 by a pair of tapered honing wheels 28 mounted for rotation about axes 30. The razor blade strip 10 is driven at uniform speed in suitable manner as indicated diagrammatically by output or takeup rolls 34.

In the illustrated embodiment, the grinding operation at stage 14 and the rough honing operation at stage 20 are performed with apparatus of conventional design, that is two abrading wheels mounted opposite sides of the razor blade strip. Each pair of wheels are driven in rotation about axes that extend parallel to the edge 12 of the blade strip 10. Razor blade sharpening equipment of this type is well known in the art, an example of such equipment being illustrated and described in Delafontaine US Pat. No. 2,709,874, and reference may be had thereto for illustration and description of constructional details of this general type of apparatus. In the illustrated embodiment, the abrading wheels at the grinding stage 14 are controlled to grind the edge 12 of the strip 10 to a controlled facet that has an included angle in the range of 9l3. This facet is then smoothed by abrading wheels of finer grit mounted in the rough honing stage 20 and form a second facet having an included angle in the range of l l 1 7 and a facet length of approximately 0.005 inch.

The rough-honed blade edge 12 is then subjected to a finish honing operation at stage 26 in which the blade is subjected to an abrading operation from the ultimate tip back a distance of about 0.001 inch. This finish honing operation provides a convex facet surface 24 as illustrated in the diagram of FIG. 6 which has an included angle in the order of 28 at the ultimate blade tip. The configuration of the curved facet surface 36 may be contrasted with the substantially straight final facet surface 38 of the conventionally finish honed blade shown in FIG. 5.

This convex configuration of the final facet 36 is produced by the final honing stage 26 through the use of two honing wheels 28 of modified frustoconical configuration that are mounted for rotation about parallel axes that are inclined at a tilt angle of about relative to the blade path as defined by blade holder 40 as indicated in FIGS. 24. Each honing wheel 28 is manufactured of a suitably fine grade of abrasive material such as silicon carbide, alumina, diamond, or a combination of such materials. Each wheel 28 in this embodiment has a length of 5 inches and a radius (r,) at its larger end (point A) of 2.800 inches; and a radius (r at its smaller end (point C) of 2.712 inches. Each wheel 28 is mounted on a spindle 42 that includes bearing mounts 44, 46, the centers of which are spaced 14 inches apart. A drive gear 48 is positioned on each spindle between bearing mount 44 and the honing wheel 28. The spindles 42 are mounted in suitable bearing blocks (not shown) for rotation about parallel axes that are inclined at 5 with respect to the direction of travel of blade as guided by support 40 as indicated in FIGS. 1 and 3. The circumferential surface of each wheel 28 has a spiral helix formed on it to define a series of lands 50. The wheels are mounted so that these lands are interengaged and define a nip 52 through which the strip 10 passes as indicated in FIG. 4. Conventional arrangements (not shown) for cooling and lubricating the strip 10 and the honing wheels 28 are provided.

A diagrammatic view illustrating the geometry of one of the wheels 28 relative to the edge 12 of the blade 10 as indicated in FIG. 7. In that FIG. the larger or entrance circumference of the finish honing wheel is indicated by arc 60, and the smaller or exit circumference of the honing wheel is indicated by arc 62. An intermediate circumference is indicated by dotted line 64. The path of the blade edge 12 is along a straight line perpendicular to line 66 and to the paper. The axis of spindle 42 is indicated by line 68 and the position of that axis in the longitudinal direction at the entrance end of the honing wheel is indicated at point A while the position of that axis at the exit end of the wheel is indicated at point C.

As the' intersection of the frustoconical surfaces of wheels 28 (if their tapers were straight) is a hyperboloid (the deviation from a straight line at the middle of the wheel is about 0.0085 inch over the 5-inch length in the above-described embodiment) it is desirable to modify the configuration of the surfaces of the honing wheels slightly to provide a straight line of intersection between those wheels. In the preferred embodiment, this modification is accomplished by mounting the spindle 42 carrying an abrasive honing wheel 28, in a thread grinding machine of the type indicated in FIGS. 8-10 and dressing the finish honing wheel 28 by use of a dressing wheel which is moved in a generally transverse direction relative to the spindle 42. As indicated in FIGS. 8-l0 there is provided a dressing wheel 70, 17.8 inches in diameter which is mounted for rotation about axis 72. Disposed adjacent dressing wheel 70 is table 74 on which carriage 76 is mounted for movement in a direction parallel to axis 72. Mounted on carriage 76 is a fixed tail stock structure 78 and an adjustable head stock structure 80. The spindle 42 carrying the finish honing wheel 28 to be dressed is positioned with its ends supported in the tail and head stocks 78,80 respectively, and with its drive gear 48 in engagement with a suitable drive 82 (indicated diagrammatically) so that the spindle may be rotated by drive motor 84.

With reference to the geometric diagram of FIG. 11, the coordinates of the position of the head stock 80 relative to the dressing wheel 70 involves decisions as to the angle of honing at the entrance end (a1 FIG. 7); the angle of honing at the exit end ((1 FIG. 7); and the radius r that will cut the entry angle (some arbitrary radius less than that which exists in the wheel to be dressed).

The radius r of the small end of the wheel then is determined from the equation:

The elevation of the center of the large radius end of the wheel above the small radius end is determined from the equation:

r sin (01 -04 cos a;

The angle of tilt (I; then machined into the head is determined where 'r= length of wheel face:

r =r (f/2) 2 r (f/2) cosB r, =r +f2 r fcosfi multiply (4) by 2 and subtract (5) FIG. 11 is a schematic view transverse to the bed length of the thread grinder where w radius of the dressing wheel and r r and r;, are the abrasive wheel radii from FIG. 7. The axis of the wheel-mounted-spindle 42 is indicated in projection by the line I-J measured from the ends of the spindle 42. The angular positioning of this axis (the purpose of this calculation) is determined by the vertical coordinate g (the elevation of the entry end of the honing wheel spindle over the exit end) and the horizontal coordinate m. The exit spindle end I is posifor EMP: b h /4 c hc cos A Multiply 8 by 2 and subtract( 7 The values of the side of triangle EPI in FIG. 11 must be obtained in order to calculate the angles 1 and then and thence 3 From proportional relationships (FIG. 3):

.a Z T t (12) and where 0 is the distance from the small end of the wheel 28 on the spindle to the center I of bearing 44 that couples the fixed center point of the thread grinder with the spindle end; I is the distance between the centers 1, J of bearings 44, 46 of the spindle 42; t is the length of abrasive wheel 28; and h was calculated in equation (9).

From the triangle EPI in FIG. 11 and the law of cosines e =c +i -2 01' 00s 0 (l4) sin a=c0s Eliminating e from (14) cos Y 0 sin '0 w/c +'i -2ci cos 0 (16) sin c0s a-Lilcioia Again eliminating 6 sin y: z'c cos 0 x c +z' 2ci cos 0 (18) Therefore in triangle IJG in Fig. 11 and from equations (12), (13) and (18):

m= horizontal coordinate= v c +z' 2ci cos 6 (19) g=vertical coordinate= no sin 0 /c +i 2ci cos 0 (20) A calculation based upon the above formulation is performed as follows:

A decision is made that the entry angle a 1 is to be 16 and that a drop of 9 will be provided across the finish hone wheel of length (r) of 5 inches so that a 3 is 7. The wheel as furnished has a 3-inch radius which will be dressed down to an entry radius r of 2.8 inches.

From equations 1 r =2.7ll74 2 f=0.441307" (6) r =2.74738" By adding the dressing wheel radius w 8.9 inches) to the values of r r and r we obtain:

From equations (9) h=0.893962" cos 0=0.0606l0" Solving equation- (10) sin 0=0.998162" From equations (12) i=l.555l0" (l3) n=3.l9950" (19) m=0.2344" (20) g=3.l909" The honing wheel 28 and spindle 42 is therefore mounted on the thread-grinder bed 74 so that the spindle end 46 near the large wheel diameter is positioned up 3.1909 inches and in (toward the dressing wheel) 0.2344 inches. The 8.9 inch radius dressing wheel 70 is then fed into and across the rotating wheel-mounted-spindle 42 until the operator measures a diameter of 5.600 inches at the large wheel end.

It is desirable to chamfer the corners of the lands 50 to minimize the effect of transition between adjacent lands of the interengaged honing wheels 28 on the edge 12 of the blade 10. Further it is desirable to condition the honing wheels 28 by operation under relatively heavy feed conditions on a series of blades in a breakin operation prior to actual assembly of the honing wheels 28 into the sharpening line. Two finish honing wheels 28, configured and conditioned in the above-described manner, are then mounted at stage 26 in bearing blocks so that their axes are parallel and inclined at an angle of 5 with respect to the blade holder 40. The precise honing head setting is determined by applying a suitable pressure indicating medium (such as a grease) to the honing wheels and gently feeding the wheels into the blade edge 12. The settings of the spindles 42 are then adjusted to obtain uniform blade edge contact over the entire length of the wheels.

A blade strip 10 is fed through the sharpening apparatus at a speed of 40 feet per minute and the honing wheels 28 are rotated to contact the blade edge 12 from opposite sides in a downward direction. As indicated above, this honing operation provides a curved facet configuration of the type indicated in FIG. 6. In processing thin stainless steel strip, 0.0015 inch in thickness, an included angle of about 28 at the ultimate tip is obtained. The final facet surfaces produced by this apparatus and method are smoothly curved, convex facets, free of major distortion as the distorting effect of final honing wheel contact on the thin blade stock at the output end ofthe finish honing stage 26 is eliminated.

While a particular embodiment of the invention has been shown and described, various modifications thereof will be obvious to those skilled in the art and therefore it is not intended that the invention be limited to the disclosed embodiment or to details thereof and departures may be made therefrom within the spirit and scope of the invention as defined in the claims.

We claim:

1. A method for modifying the surface configuration of a tapered abrading wheel comprising the steps of providing a support for said abrading wheel adjacent a dressing wheel, offsetting the axis of said abrading wheel relative to the axis of said dressing wheel in vertical and horizontal directions and fixing the axis of said abrading wheel at a location parallel to a line that does not intersect and is not parallel to said axis of said dressing wheel, said dressing wheel axis being related to said line such that rotation of said dressing wheel axis about said line would generate a true hyperboloid of revolution; and simultaneously rotating said abrading and said dressing wheels 

1. A method for modifying the surface configuration of a tapered abrading wheel comprising the steps of providing a support for said abrading wheel adjacent a dressing wheel, offsetting the axis of said abrading wheel relative to the axis of said dressing wheel in vertical and horizontal directions and fixing the axis of said abrading wheel at a location parallel to a line that does not intersect and is not parallel to said axis of said dressing wheel, said dressing wheel axis being related to said line such that rotation of said dressing wheel axis about said line would generate a true hyperboloid of revolution; and simultaneously rotating said abrading and said dressing wheels about thEir respective axes while the surfaces of said abrading and dressing wheels are in contact to modify the surface of said abrading wheel so that that surface closely approximates a portion of a true hyperboloid of revolution.
 2. The method as claimed in claim 1 wherein said abrading wheel and said dressing wheel are moved relative to one another during said modification operation along an axis parallel to the axis of said dressing wheel. 